Strengthened glass, strengthened glass plate, strengthened glass container, and glass for strengthening

ABSTRACT

To devise a tempered glass and a glass to be tempered each of which is lowered in density and viscosity at high temperature, hardly deteriorates a KNO 3  molten salt, and is excellent in thermal shock resistance. The tempered glass having a compression stress layer in a surface thereof, including as a glass composition, in terms of mol %, 50 to 80% of SiO 2 , 5 to 30% of Al 2 O 3 , 0 to 2% of Li 2 O, 5 to 25% of Na 2 O, and 0 to 5% of K 2 O, and being substantially free of As 2 O 3 , Sb 2 O 3 , PbO, and F.

TECHNICAL FIELD

The present invention relates to a tempered glass, a tempered glass sheet, and a glass to be tempered, in particular, to a tempered glass, a tempered glass sheet, and a glass to be tempered suitable for a cover glass for a cellular phone, a digital camera, a personal digital assistant (PDA), or a solar battery, or a glass substrate for a display, in particular, a touch panel display. Further, the present invention relates to a tempered glass container, in particular, a tempered glass container for use as a container for pharmaceuticals.

BACKGROUND ART

Devices such as a cellular phone, a digital camera, a PDA, a touch panel display, a large-screen television, and contact-less power transfer show a tendency of further prevalence.

A tempered glass, which is produced by applying tempering treatment to glass through ion exchange treatment or the like, is used for those applications (see Patent Literature 1 and Non Patent Literature 1).

In addition, in recent years, the tempered glass has been more and more frequently used in exterior parts of, for example, digital signage, mice, and smartphones.

A related-art device includes a display module, a touch panel sensor, and the tempered glass (protective member). In recent years, a method involving forming the touch panel sensor on the tempered glass has started to be adopted in order to achieve a reduction in weight or a reduction in thickness. As a result, such protective member is required to: (1) have high mechanical strength; (2) have high flaw resistance; (3) be less costly; (4) have low density; (5) have sufficiently high acid resistance for preventing denaturation of its surface in acid treatment at the time of formation of the touch panel sensor; and (6) be free of a substance having a high environmental load.

CITATION LIST Patent Literature

-   [PTL 1] JP 2006-83045 A

Non Patent Literature

-   [NPL 1] Tetsuro Izumitani et al., “New glass and physical properties     thereof,” First edition, Management System Laboratory. Co., Ltd.,     Aug. 20, 1984, p. 451-498

SUMMARY OF INVENTION Technical Problem

Incidentally, when the content of Li₂O in a glass composition is increased, viscosity at high temperature can be lowered while ion exchange performance is enhanced. However, when the content of Li₂O is increased and ion exchange treatment is performed using a potassium nitrate molten salt (KNO₃ molten salt), a Li ion is liable to be mixed in the KNO₃ molten salt. The KNO₃ molten salt having mixed therein the Li ion makes it difficult to enhance the tempering characteristic of a glass to be tempered. As a result, the KNO₃ molten salt needs to be frequently replaced, and hence the productivity of a tempered glass is liable to lower. Further, when the content of Li₂O is increased, liquidus viscosity is liable to lower. It should be noted that a Na ion also has property of deteriorating the KNO₃ molten salt, but the degree of the deterioration is lower than that in the case of the Li ion.

In addition, hitherto, as the glass to be tempered, there has been proposed a glass containing large amounts of Na₂O and K₂O in its glass composition. However, Na₂O and K₂O are each a component that increases density. Meanwhile, when the contents of Na₂O and K₂O are decreased in order to lower the density, the viscosity at high temperature increases, with the result that the productivity of the glass is liable to lower. Thus, it has been difficult to lower both the density and the viscosity at high temperature.

Further, as the content of Li₂O, Na₂O, or K₂O increases, the thermal expansion coefficient of the glass to be tempered is liable to become higher. In addition, the ion exchange treatment is generally performed by immersing the glass to be tempered in a high-temperature (for example, from 300 to 500° C.) KNO₃ molten salt. Thus, when the Li₂O, Na₂O, or K₂O-rich glass is subjected to ion exchange treatment, the tempered glass is liable to undergo breakage owing to a thermal shock when the glass to be tempered is immersed in the KNO₃ molten salt or when the tempered glass is taken out.

In order to solve the problem, it is conceivable to employ a method involving preheating a glass sheet to be tempered before immersion in the KNO₃ molten salt, or annealing a tempered glass that has been taken out of an ion exchange tank. However, such method requires a long period of time, and hence involves a risk that the manufacturing cost of the tempered glass may soar.

The present invention has been made in view of the above-mentioned circumstances, and a technical object of the present invention is to devise a tempered glass and a glass to be tempered each of which is lowered in density and viscosity at high temperature, hardly deteriorates an ion exchange solution, in particular, a KNO₃ molten salt, and is excellent in thermal shock resistance.

Solution to Problem

The inventors of the present invention have made various studies, and as a result, have found the following. When, in a glass composition, the contents of Al₂O₃ and Na₂O are increased, and at the same time, the contents of Li₂O and K₂O are decreased, and as required, B₂O₃ is introduced and the content of MgO is decreased, while ion exchange performance does not lower, density and viscosity at high temperature lower, property of deteriorating an ion exchange solution lowers, and thermal shock resistance improves. The finding is proposed as the present invention. Thus, the finding is proposed as the present invention. That is, a tempered glass of the present invention has a compression stress layer in a surface thereof, comprises as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and is substantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the gist of the phrase “substantially free of As₂O₃” resides in that As₂O₃ is not added positively as a glass component, but contamination with As₂O₃ as an impurity is allowable. Specifically, the phrase means that the content of As₂O₃ is less than 0.1 mol %. The gist of the phrase “substantially free of Sb₂O₃” resides in that Sb₂O₃ is not added positively as a glass component, but contamination with Sb₂O₃ as an impurity is allowable. Specifically, the phrase means that the content of Sb₂O₃ is less than 0.1 mol %. The gist of the phrase “substantially free of PbO” resides in that PbO is not added positively as a glass component, but contamination with PbO as an impurity is allowable. Specifically, the phrase means that the content of PbO is less than 0.1 mol %. The gist of the phrase “substantially free of F” resides in that F is not added positively as a glass component, but contamination with F as an impurity is allowable. Specifically, the phrase means that the content of F is less than 0.1 mol %. It should be noted that when substantial addition of As₂O₃, Sb₂O₃, PbO, and F is eliminated, a closely related environmental requirement can be satisfied.

The tempered glass of the present invention preferably comprises as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 0.1 to 2.5% of MgO, and 0 to 2.5% of MgO+CaO+SrO+BaO, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the term “MgO+CaO+SrO+BaO” means the total amount of MgO, CaO, SrO, and BaO.

The tempered glass of the present invention preferably comprises as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0.01 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, and 0.1 to 2.5% of MgO+CaO+SrO+BaO, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the term “Li₂O+Na₂O+K₂O” means the total amount of Li₂O, Na₂O, and K₂O.

The tempered glass of the present invention preferably comprises as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5 of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the term “Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO” means the total amount of Li₂O, Na₂O, K₂O, MgO, CaO, SrO, and BaO.

The tempered glass of the present invention preferably comprises as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, preferably has a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F.

The tempered glass of the present invention preferably comprises as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, preferably has a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the term “Al₂O₃+B₂O₃” means the total amount of Al₂O₃ and B₂O₃.

The tempered glass of the present invention preferably has a density of 2.45 g/cm³ or less. Herein, the “density” can be measured by, for example, a known Archimedes method.

When the tempered glass of the present invention is immersed in a 10 mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, it is preferred that a mass reduction be 40 mg/cm² or less. Herein, the “mass reduction” is a mass reduction after immersion in the aqueous hydrochloric acid solution for 24 hours, and can be calculated by: first measuring the mass and surface area of an evaluation sample before its immersion in the aqueous hydrochloric acid solution; then measuring the mass of the evaluation sample after its immersion in the aqueous hydrochloric acid solution; and finally substituting the measured values into the following expression: (mass before immersion-mass after immersion)/(surface area before immersion).

In the tempered glass of the present invention, it is preferred that a compression stress value of the compression stress layer be 300 MPa or more, and a thickness of the compression stress layer be 10 μm or more. Herein, the “compression stress value of the compression stress layer” and the “thickness of the compression stress layer” refer to values calculated from the number of interference fringes and intervals therebetween, the interference fringes being observed when a sample is observed using a surface stress meter (for example, FSM-6000 manufactured by TOSHIBA CORPORATION).

The tempered glass of the present invention preferably has a liquidus temperature of 1,200° C. or less. Herein, the phrase “liquidus temperature” refers to a temperature at which crystals of glass are deposited after glass powder that passes through a standard 30-mesh sieve (sieve opening: 500 μm) and remains on a 50-mesh sieve (sieve opening: 300 μm) is placed in a platinum boat and then kept for 24 hours in a gradient heating furnace.

The tempered glass of the present invention preferably has a liquidus viscosity of 10^(4.0) dPa·s or more. Herein, the phrase “liquidus viscosity” refers to a value obtained through measurement of a viscosity of glass at the liquidus temperature by a platinum sphere pull up method.

The tempered glass of the present invention preferably has a temperature at 10^(4.0) dPa·s of 1,300° C. or less. Herein, the phrase “temperature at 10^(4.0) dPa·s” refers to a value obtained through measurement by a platinum sphere pull up method.

The tempered glass of the present invention preferably has a thermal expansion coefficient in a temperature range of from 30 to 380° C. of 90×10⁻⁷/° C. or less. Herein, the phrase “thermal expansion coefficient in a temperature range of from 30 to 380° C.” refers to a value obtained by measuring an average thermal expansion coefficient with a dilatometer.

A tempered glass sheet of the present invention preferably comprises any one of the tempered glasses.

The tempered glass sheet of the present invention preferably has a length dimension of 500 mm ox more, a width dimension of 300 mm or more, and a thickness of from 0.1 to 2.0 mm.

The tempered glass sheet of the present invention is preferably formed by an overflow down-draw method. Herein, the “overflow down-draw method” refers to a method comprising causing a molten glass to overflow from both sides of a heat-resistant forming trough, and subjecting the overflowing molten glasses to down-draw downward while the molten glasses are joined at the lower end of the forming trough, to thereby manufacture a glass sheet. In the overflow down-draw method, surfaces that are to serve as the surfaces of the glass sheet are formed in a state of free surfaces without being brought into contact with the surface of the forming trough. Accordingly, a glass sheet having satisfactory surface quality in an unpolished state can be manufactured at low cost.

The tempered glass sheet of the present invention is preferably used for a touch panel display.

The tempered glass sheet of the present invention is preferably used for a cover glass for a cellular phone.

The tempered glass sheet of the present invention is preferably used for a cover glass for a solar battery.

A tempered glass sheet of the present invention is a tempered glass sheet having a length dimension of 500 mm or more, a width dimension of 300 mm or more, and a thickness of from 0.1 to 2.0 mm, characterized in that: the tempered glass sheet comprises as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 1.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, has a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and is substantially free of As₂O₃, Sb₂O₃, PbO, and F; and the tempered glass sheet has a density of 2.45 g/cm³ or less, a compression stress value of a compression stress layer of 300 MPa or more, a thickness of the compression stress layer of 10 μm or more, a liquidus temperature of 1,200° C. or less, and a thermal expansion coefficient in a temperature range of from 30 to 380° C. of 90×10⁻⁷ or less.

A tempered glass container of the present invention comprises the tempered glass. Further, the tempered glass container of the present invention is preferably used for a container for pharmaceuticals.

As a container to be filled for storing a pharmaceutical, there has been used a glass container in the form of an ampule, a vial, a prefilled syringe, a cartridge, or the like. In recent years, along with progress in pharmacy and medicine, the number of cases where the glass container is filled with an expensive drug has been increasing. However, the glass container may break in a manufacturing process at a pharmaceutical company, or at a clinical site. When the glass container filled with an expensive drug breaks, not only the loss of the drug itself, but also a production loss involved in the interruption of a manufacturing line occurs, resulting in an extremely significant total loss in cost. Further, the breakage of the glass container also generates a safety risk.

A flaw present in the glass container is a cause for the breakage of the glass container. The flaw is generated in each of various steps such as container processing, inspection, transportation, and drug filling. Therefore, the glass container to be used for a pharmaceutical is required to have flaw resistance, and because of the nature of its application, is also required to have acid resistance and be free of an environmental load substance. Accordingly, the tempered glass (tempered glass container) of the present invention, which is excellent in flaw resistance and acid resistance, and is substantially free of As₂O₃, Sb₂O₃, PbO, and F, is suitable for this application.

A glass to be tempered of the present invention preferably comprises as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F.

When the tempered glass of the present invention is immersed in a 10 mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, it is preferred that a mass reduction be 40 mg/cm² or less.

The glass to be tempered of the present invention preferably has a ratio CS₂/CS₁ of a compression stress value CS₂ to a compression stress value CS₁ of 0.7 or more, the compression stress value CS₁ being determined for a compression stress layer that is obtained by subjecting the glass to be tempered to ion exchange treatment in a potassium nitrate molten salt free of a history of being used, the compression stress value CS₂ being determined for a compression stress layer that is obtained by subjecting the glass to be tempered to ion exchange treatment in a potassium nitrate molten salt comprising 20,000 ppm (by mass) of Na ions. It should be noted that in the calculation of the CS₂/CS₁, an ion exchange temperature is set to 430° C. and an ion exchange time is set to 4 hours.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a is a schematic plan view illustrating a first example of the attachment state of a protective resin film with respect to a glass sheet to be tempered according to an embodiment of the present invention.

FIG. 1 b is a schematic plan view illustrating a second example of the attachment state of the protective resin film with respect to the glass sheet to be tempered according to the embodiment of the present invention.

FIG. 1 c is a schematic plan view illustrating a third example of the attachment state of the protective resin film with respect to the glass sheet to be tempered according to the embodiment of the present invention.

FIG. 1 d is a schematic plan view illustrating a fourth example of the attachment state of the protective resin film with respect to the glass sheet to be tempered according to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

A tempered glass of the present invention has a compression stress layer in a surface thereof. A method of forming the compression stress layer in the surface includes a physical tempering method and a chemical tempering method. The tempered glass of the present invention is preferably produced by the chemical tempering method.

The chemical tempering method is a method involving introducing alkali ions each having a large ion radius into the surface of glass by ion exchange treatment at a temperature equal to or lower than a strain point of the glass. When the chemical tempering method is used to form a compression stress layer, the compression stress layer can be properly formed even in the case where the thickness of the glass is small. In addition, even when a tempered glass is cut after the formation of the compression stress layer, the tempered glass does not easily break unlike a tempered glass produced by applying a physical tempering method such as an air cooling tempering method.

Described below are reasons why the content ranges of the respective components in the tempered glass of the present invention are restricted as described above. It should be noted that in the description of the content range of each component, the expression “%” means “mol.” unless otherwise specified.

SiO₂ is a component that forms a network of glass, and the content of SiO₂ is from 50 to 80%, and is preferably from 55 to 77%, from 57 to 75%, from 58 to 74%, from 60 to 73%, or from 62 to 72%. When the content of SiO₂ is too small in glass, vitrification does not occur easily, the acid resistance of the glass reduces, the thermal expansion coefficient becomes too high, and the thermal shock resistance easily lowers. On the other hand, when the content of SiO₂ is too large in glass, the meltability and formability easily lower, and the thermal expansion coefficient becomes too low, with the result that it becomes difficult to match the thermal expansion coefficient with those of peripheral materials. It should be noted that when the content of SiO₂ is decreased and the content of B₂O₃ is increased, density and viscosity at high temperature can both be easily lowered, but at the same time, the acid resistance lowers, and hence it is difficult to apply the tempered glass to an acid treatment step at the time of the formation of a touch panel sensor.

Al₂O₃ is a component that enhances the ion exchange performance of glass and a component that enhances the strain point or Young's modulus, and the content of Al₂O₃ is from 5 to 30%. When the content of Al₂O₃ is too small in glass, the ion exchange performance may not be exhibited sufficiently. Thus, a suitable lower limit range of the content of Al₂O₃ is 5.5% or more, 6% or more, 6.5% or more, 7% or more, 8% or more, or 9% or more. On the other hand, when the content of Al₂O₃ is too large in glass, the density of the glass easily increases and devitrified crystals are easily deposited in the glass, and it becomes difficult to form a glass sheet by an overflow down-draw method or the like. Further, the thermal expansion coefficient of the glass becomes too low, and it becomes difficult to match the thermal expansion coefficient with those of peripheral materials. In addition, the acid resistance also lowers, which makes it difficult to apply the tempered glass to an acid treatment step at the time of the formation of a touch panel sensor. Further, viscosity at high temperature increases, which is liable to lower meltability. Thus, a suitable upper limit range of the content of Al₂O₃ is 25% or less, 20% or less, 18% or less, 16% or less, 15% or less, 14% or less, 13.5% or less, 13.4% or less, 13% or less, 12.5% or less, or 12.4% or less.

Li₂O is an ion exchange component and is a component that lowers the viscosity at high temperature of glass to increase the meltability and the formability, and increases the Young's modulus. However, Li₂O is a component that deteriorates an ion exchange solution. Further, Li₂O has a great effect of increasing the compression stress value of glass among alkali metal oxides, but when the content of Li₂O becomes extremely large in a glass system containing Na₂O at 7% or more, the compression stress value tends to lower contrarily. Further, when the content of Li₂O is too large in glass, the liquidus viscosity lowers, easily resulting in the devitrification of the glass, and the thermal expansion coefficient becomes too high, with the result that the thermal shock resistance lowers and it becomes difficult to match the thermal expansion coefficient with those of peripheral materials. In addition, the viscosity at low temperature of the glass becomes too low, and the stress relaxation occurs easily, with the result that the compression stress value lowers contrarily in some cases. Thus, the content of Li₂O is 2% or less, and is preferably 1.7% or less, 1.5% or less, 1% or less, less than 1%, 0.5% or less, 0.3% or less, 0.2% or less, or 0.1% or less.

Na₂O is an ion exchange component and is a component that lowers the viscosity at high temperature of glass to increase the meltability and formability. Na₂O is also a component that improves the devitrification resistance of glass. When the content of Na₂O is too small in glass, the meltability lowers, the thermal expansion coefficient unreasonably lowers, and the ion exchange performance is liable to lower. Thus, the content of Na₂O is 5% or more, and a suitable lower limit range thereof is 7% or more, more than 7.0%, 8% or more, or 9% or more. On the other hand, when the content of Na₂O is too large in glass, there is a tendency that the density increases and the thermal expansion coefficient becomes too high, with the result that the thermal shock resistance lowers, it becomes difficult to match the thermal expansion coefficient with those of peripheral materials, and the density increases. Further, the strain point lowers excessively, and the glass composition loses its component balance, with the result that the devitrification resistance lowers contrarily in some cases. Further, the ion exchange solution is liable to deteriorate. Thus, the content of Na₂O is 25% or less, and a suitable upper limit range thereof is 23% or less, 21% or less, 19% or less, 18.5% or less, 17% or less, 16% or less, 15.5% or less, 14% or less, 13.5% or less, or 13% or less.

K₂O is a component that promotes ion exchange and is a component that allows the thickness of a compression stress layer to be easily enlarged among alkali metal oxides. K₂O is also a component that lowers the viscosity at high temperature of glass to increase the meltability and formability. K₂O is also a component that improves devitrification resistance. However, when the content of K₂O is too large, the density of glass increases, the thermal expansion coefficient of the glass becomes too large, the thermal shock resistance of the glass lowers, and it becomes difficult to match the thermal expansion coefficient with those of peripheral materials. Further, the strain point lowers excessively, and the glass composition loses its component balance, with the result that the devitrification resistance tends to lower contrarily. Thus, a suitable upper limit range of the content of K₂O is 5% or less, 4% or less, 3.5% or less, or 3% or less. It should be noted that when K₂O is added, a suitable addition amount is 0.1% or more, 0.5% or more, or 1% or more. In addition, when the addition of KO is avoided as much as possible, the suitable addition amount is 1.9% or less, 1.35% or less, 1% or less, or less than 1%, particularly preferably 0.05% or less.

When the content of Li₂O+Na₂O+K₂O is excessively low, the ion exchange performance and the meltability are liable to lower. Thus, a suitable lower limit range of the content of Li₂O+Na₂O+K₂O is 5% or more, 9% or more, 10% or more, 11% or more, 12% or more, 131 or more, or 14% or more. On the other hand, when the content of Li₂O+Na₂O+K₂O is excessively high, there is a tendency that the thermal expansion coefficient increases excessively, with the result that the thermal shock resistance lowers, it becomes difficult to match the thermal expansion coefficient with those of peripheral materials, and the density increases. There is also a tendency that the strain point lowers excessively and the component balance of the glass composition is lost, with the result that the devitrification resistance lowers contrarily. Thus, a suitable upper limit range of the content of Li₂O+Na₂O+K₂O is 30% or less, 19% or less, 18.5 or less, 18% or less, 17.5% or less, 17% or less, or 16.5% or less.

For example, the following components other than the components may be added.

The content of B₂O₃ is preferably from 0 to 15%. B₂O₃ is a component that lowers the viscosity at high temperature and density of glass, stabilizes the glass so that a crystal may be unlikely precipitated, and lowers the liquidus temperature of the glass. In addition, B₂O₃ is a component that enhances crack resistance to enhance flaw resistance. Thus, a suitable lower limit range of the content of B₂O₃ is 0.01% or more, 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, 4% or more, 5′% or more, 5.5% or more, or 6% or more. However, when the content of B₂O₃ is too large, the acid resistance of glass may reduce, coloring on the surface of the glass called weathering may occur through ion exchange, water resistance may lower, and the thickness of a compression stress layer is liable to decrease. Thus, a suitable upper limit range of the content of B₂O₃ is 14% or less, 13% or less, 12% or less, 11% or less, less than 10.5%, 10% or less, 9% or less, or 8% or less.

MgO is a component that reduces the viscosity at high temperature of glass to enhance the meltability and formability, and increases the strain point and Young's modulus, and is a component that has a great effect of enhancing the ion exchange performance among alkaline earth metal oxides. Thus, a suitable lower limit range of the content of MgO is 0.01% or more, 0.05% or more, or 0.1% or more, particularly preferably 0.5% or more. However, when the content of MgO is too large in glass, the density and thermal expansion coefficient easily increase, and the devitrification of the glass tends to occur easily. Thus, a suitable upper limit range of the content of MgO is 3% or less, 2.7% or less, 2.5% or less, 2.2% or less, 2% or less, 1.5% or less, or 1% or less.

CaO has greater effects of reducing the viscosity at high temperature of glass to enhance the meltability and formability, and increasing the strain point and Young's modulus without involving a reduction in devitrification resistance as compared to other components. However, when the content of CaO is too large in glass, the density and thermal expansion coefficient increase, and the glass composition loses its component balance, with the result that the glass is liable to devitrify contrarily, the ion exchange performance lowers, and the deterioration of an ion exchange solution occurs easily. Thus, the content of CaO is preferably from 0 to 6%, from 0 to 5%, from 0 to 4%, from 0 to 3.5, from 0 to 3%, from 0 to 2%, or from 0 to 1.

SrO is a component that reduces the viscosity at high temperature of glass to enhance the meltability and formability, and increases the strain point and Young's modulus. However, when the content thereof is too large in glass, an ion exchange reaction is liable to be inhibited, and moreover, the density and thermal expansion coefficient increase, and the devitrification of the glass occurs easily. Thus, the content of SrO is preferably from 0 to 1.5%, from 0 to 1%, from 0 to 0.5%, from 0 to 0.1%, or from 0 to less than 0.1%.

BaO is a component that reduces the viscosity at high temperature of glass to enhance the meltability and formability, and increases the strain point and Young's modulus. However, when the content of BaO is too large in glass, an ion exchange reaction is liable to be inhibited, and moreover, the density and thermal expansion coefficient increase, and the devitrification of the glass occurs easily. Thus, the content of BaO is preferably from 0 to 6%, from 0 to 3%, from 0 to 1.5%, from 0 to 1%, from 0 to 0.5%, from 0 to 0.1%, or from 0 to less than 0.1%.

When the content of MgO+CaO+SrO+BaO is excessively high, there is a tendency that the density and the thermal expansion coefficient increase, the glass devitrifies, and the ion exchange performance lowers. Thus, a suitable upper limit range of the content of MgO+CaO+SrO+BaO is 9.9% or less, 6.5% or less, 5% or less, 3% or less, 2.8% or less, 2.7% or less, 2.5% or less, 2.2% or less, 2% or less, 1.5% or less, or 1% or less. On the other hand, when the content of MgO+CaO+SrO+BaO is excessively low, the meltability and the formability are liable to lower, and the strain point and the Young's modulus are liable to lower. Thus, a suitable lower limit range of the content of MgO+CaO+SrO+BaO is 0.01% or more, 0.05% or more, 0.1% or more, or 0.5% or more.

When the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is excessively low, the meltability is liable to lower. Thus, a suitable lower limit range of the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is 10% or more, 12% or more, 13% or more, or 14% or more. On the other hand, when the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is excessively high, there is a tendency that the density and the thermal expansion coefficient increase, and the ion exchange performance lowers. Thus, a suitable upper limit range of the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is 30% or less, 25% or less, 23% or less, 21% or less, 20% or less, 19% or less, 18.5% or less, or 18% or less.

When a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) reduces, the ion exchange performance tends to lower, and the thermal expansion coefficient is liable to increase. Thus, a suitable lower limit range of the molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) is 0.001 or more, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more. On the other hand, when the molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) increases, the devitrification resistance is liable to lower, and the glass is liable to undergo phase separation. Thus, a suitable upper limit range of the molar ratio MgO/(Li₂O+Na₂O+K?O+MgO+CaO+SrO+BaO) is 0.5 or less, 0.3 or less, 0.25 or less, 0.2 or less, 0.15 or less, 0.1 or less, 0.09 or less, 0.08 or less, or 0.07 or less.

When a molar ratio (Al₂O₃+B₂O₃)/SiO₂ reduces, the crack resistance is liable to lower, and the meltability and the formability are liable to lower. Thus, a suitable lower limit range of the molar ratio (Al₂O₃+B₂O₃)/SiO₂ is 0.1 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, 0.19 or more, or 0.2 or more. On the other hand, when the molar ratio (Al₂O₃+B₂O₃)/SiO₂ increases, the devitrification resistance is liable to lower, the glass is liable to undergo phase separation, and the acid resistance is liable to lower. Thus, a suitable upper limit range of the molar ratio (Al₂O₃+B₂O₃)/SiO₂ is 0.5 or less, 0.4 or less, 0.35 or less, 0.32 or less, 0.31 or less, 0.30 or less, 0.29 or less, 0.28 or less, 0.27 or less, or 0.26 or less.

A molar ratio B₂O₃/Al₂O₃ is preferably from 0 to 1, from 0.1 to 0.6, from 0.12 to 0.5, from 0.142 to 0.37, from 0.15 to 0.35, from 0.18 to 0.32, or from 0.2 to 0.3. This allows both the devitrification resistance and the ion exchange performance to be achieved at high levels while the viscosity at high temperature is optimized.

A molar ratio B₂O₃/(Na₂O+Al₂O₃) is preferably from 0 to 1, from 0.01 to 0.5, from 0.02 to 0.4, from 0.03 to 0.3, from 0.03 to 0.2, from 0.04 to 0.18, from 0.05 to 0.17, from 0.06 to 0.16, or from 0.07 to 0.15. This allows both the devitrification resistance and the ion exchange performance to be achieved at high levels while the viscosity at high temperature is optimized.

TiO₂ is a component that enhances the ion exchange performance of glass and is a component that reduces the viscosity at high temperature. However, when the content of TiO₂ is too large in glass, the glass is liable to be colored and to devitrify. Thus, the content of TiO₂ is preferably from 0 to 4.5%, from 0 to 1%, from 0 to 0.5%, from 0 to 0.3%, from 0 to 0.1%, from 0 to 0.05%, or from 0 to 0.01%.

ZrO₂ is a component that enhances the ion exchange performance of glass, and is a component that increases the viscosity of glass around the liquidus viscosity and the strain point. Thus, a suitable lower limit range of the content of ZrO₂ is 0.001% or more, 0.005% or more, 0.01% or more, or 0.05% or more. However, when the content of ZrO₂ is excessively high, there is a risk that the devitrification resistance may lower markedly and the crack resistance may lower, and there is also a risk that the density may increase excessively. Thus, a suitable upper limit range of the content of ZrO₂ is 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, 0.3% or less, or 0.1% or less.

ZnO is a component that enhances the ion exchange performance of glass and is a component that has a great effect of increasing the compression stress value, in particular. Further, ZnO is a component that reduces the viscosity at high temperature of glass without reducing the viscosity at low temperature. However, when the content of ZnO is too large in glass, there is a tendency that the glass undergoes phase separation, the devitrification resistance lowers, the density increases, and the thickness of the compression stress layer in the glass decreases. Thus, the content of ZnO is preferably from 0 to 6%, from 0 to 5%, from 0 to 3%, or from 0 to 1%.

P₂O₅ is a component that enhances the ion exchange performance of glass and is a component that increases the thickness of the compression stress layer, in particular. However, when the content of P₂O₅ is too large in glass, the glass undergoes phase separation, and the water resistance is liable to lower. Thus, the content of P₂O₅ is preferably from 0 to 10%, from 0 to 3%, from 0 to 1%, from 0 to 0.5%, or from 0 to 0.1%.

SnO₂ has an effect of enhancing ion exchange performance. Thus, the content of SnO₂ is preferably from 0 to 3%, from 0.01 to 3%, from 0.05 to 3%, from 0.1 to 3%, or from 0.2 to 3%.

As a fining agent, one kind or two or more kinds selected from the group consisting of Cl, SO₃, and CeO₂ (preferably the group consisting of Cl and SO₃) may be added at 0 to 3%.

The content of SnO₂+SO₃+Cl is preferably from 0.01 to 3%, from 0.05 to 3%, from 0.1 to 3%, or from 0.2 to 3% from the viewpoint of simultaneously achieving a fining effect and an effect of enhancing ion exchange performance. It should be noted that the term “SnO₂+SO₃+Cl” refers to the total amount of SnO₂, Cl, and SO₃.

The content of Fe₂O₃ is preferably less than 1,000 ppm (less than 0.1%), less than 800 ppm, less than 600 ppm, less than 400 ppm, or less than 300 ppm. Further, the molar ratio Fe₂O₃/(Fe₂O₃+SnO₂) is controlled to preferably 0.8 or more, 0.9 or more, or 0.95 or more, while the content of Fe₂O₃ is controlled in the above-mentioned range. As a result, the transmittance (400 nm to 770 nm) of glass having a thickness of 1 mm is likely to improve (by, for example, 90% or more).

A rare earth oxide such as Nb₂O₅ or La₂O₃ is a component that enhances the Young's modulus. However, the cost of the raw material itself is high, and when the rare earth oxide is added in a large amount, the devitrification resistance is liable to deteriorate. Thus, the content of the rare earth oxide is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, or 0.1% or less.

The tempered glass of the present invention is substantially free of As₂O₃, Sb₂O₃, PbO, and F as a glass composition from the standpoint of environmental considerations. In addition, the tempered glass is preferably substantially free of Bi₂O₃ from the standpoint of environmental considerations. The gist of the phrase “substantially free of Bi₂O₃” resides in that Bi₂O₃ is not added positively as a glass component, but contamination with Bi₂O₃ as an impurity is allowable. Specifically, the phrase means that the content of Bi₂O₃ is less than 0.05%.

In the tempered glass of the present invention, the suitable content range of each component can be appropriately selected to attain a suitable glass composition range. Of those, particularly suitable glass composition ranges are as described below.

(1) A glass composition comprising, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F. (2) A glass composition comprising, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1.7% of Li₂O, more than 7.0 to 15.5% of Na₂O, 0 to 3.5% of K₂O, and 0 to 2.5% of MgO, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F. (3) A glass composition comprising, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 0.1 to 2.5% of MgO, and 0 to 2.5% of MgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F. (4) A glass composition comprising, in terms of mol, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0.01 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, and 0.1 to 2.5% of MgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F. (5) A glass composition comprising, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 13.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, and being substantially free of As₂O₂, Sb₂O₃, PbO, and F. (6) A glass composition comprising, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F. (7) A glass composition comprising, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.

The tempered glass of the present invention preferably has the following properties, for example.

The tempered glass of the present invention has a compression stress layer in the surface thereof. The compression stress value of the compression stress layer is preferably 300 MPa or more, 400 MPa or more, from 500 MPa to 1,500 MPa, or 500 MPa or more and less than 900 MPa. As the compression stress value becomes larger, the mechanical strength of the tempered glass becomes higher. It should be noted that there is a tendency that the compression stress value is increased by increasing the content of Al₂O₃, MgO, ZnO, TiO₂, or ZrO₂ in the glass composition or by decreasing the content of SrO or BaO in the glass composition. Further, there is a tendency that the compression stress value is increased by shortening a time necessary for ion exchange or by decreasing the temperature of an ion exchange solution. It should be noted that when the compression stress value of the compression stress layer is excessively large, its internal tensile stress becomes excessively high, with the result that the tempered glass is liable to undergo spontaneous breakage.

The thickness of the compression stress layer is preferably 10 μm or more, 15 μm or more, 15 μm or more and less than 80 μm, or 15 μm or more and 60 μm or less. As the thickness of the compression stress layer becomes larger, the tempered glass is more hardly cracked even when the tempered glass has a deep flaw, and a variation in the mechanical strength of the tempered glass becomes smaller. It should be noted that there is a tendency that the thickness of the compression stress layer is increased by increasing the content of K₂O or P₂O₅ in the glass composition or decreasing the content of SrO or BaO in the glass composition. In addition, there is a tendency that the thickness of the compression stress layer is increased by lengthening an ion exchange time or by increasing the temperature of an ion exchange solution. It should be noted that when the thickness of the compression stress layer is excessively large, its internal tensile stress becomes excessively high, with the result that the tempered glass is liable to undergo spontaneous breakage.

The tempered glass of the present invention has a density of preferably 2.6 g/cm³ or less, 2.55 g/cm³ or less, 2.50 g/cm³ ox less, 2.48 g/cm³ or less, 2.45 g/cm³ or less, 2.43 g/cm³ or less, 2.42 g/cm³ or less, 2.41 g/cm³ or less, or 2.40 g/cm³ or less. As the density becomes smaller, the weight of the tempered glass can be reduced more. It should be noted that the density is easily reduced by increasing the content of SiO₂, B₂O₃, or P₂O₅ in the glass composition or by decreasing the content of an alkali metal oxide, alkaline earth metal oxide, ZnO, ZrO₂, or TiO₂ in the glass composition.

The tempered glass of the present invention has a thermal expansion coefficient in a temperature range of from 30 to 380° C. of preferably 100×10⁻⁷/° C. or less, 95×10⁻⁷/° C. or less, 93×10⁻⁷/° C. or less, 90×10⁻⁷/° C. or less, 88×10⁻⁷/° C. or less, 85×10⁻⁷/° C. or less, 83×10⁻⁷/° C. or less, 82×10⁻⁷/° C. or less, 80×10⁻⁷/C or less, 79×10⁻⁷/° C. or less, 78×10⁻⁷/° C. or less, or from 50×10⁻⁷ to 77×10⁻⁷/° C. When the thermal expansion coefficient is regulated within the above-mentioned range, the thermal, shock resistance improves, and hence the time required for preheating before tempering treatment or annealing after the tempering treatment can be shortened. As a result, the productivity of the tempered glass can be enhanced. In addition, the thermal expansion coefficient can be easily matched with that of a member such as a metal or an organic adhesive, which makes it easy to prevent the detachment of the member such as the metal or the organic adhesive. In particular, when the thermal expansion coefficient is regulated within the above-mentioned range, in the case of using the tempered glass for a tempered glass container, its breakage due to a thermal shock in a heat treatment process in, for example, a glass tube-manufacturing step, processing step, or sterilizing step can be easily prevented. It should be noted that an increase in the content of an alkali metal oxide or alkaline earth metal oxide in the glass composition is likely to increase the thermal expansion coefficient, and conversely, a reduction in the content of the alkali metal oxide or alkaline earth metal oxide is likely to lower the thermal expansion coefficient.

The tempered glass of the present invention has a temperature at 10^(4.0) dPa·s of preferably 1,300° C. or less, 1,280° C. or less, 1,250° C. or less, 1,220° C. or less, or 1,200° C. or less. As the temperature at 10^(4.0) dPa·s becomes lower, a burden on a forming facility is reduced more, the forming facility has a longer life, and consequently, the manufacturing cost of the tempered glass is more likely to be reduced. It should be noted that the temperature at 10^(4.0) dPa·s is easily decreased by increasing the content of an alkali metal oxide, an alkaline earth metal oxide, ZnO, B₂O₃, or TiO₂ or by reducing the content of SiO₂ or Al₂O₃.

The tempered glass of the present invention has a temperature at 10^(2.5) dPa·s of preferably 1,650° C. or less, 1,600° C. or less, 1,580° C. or less, or 1,550° C. or less. As the temperature at 10^(2.5) dPa·s becomes lower, melting at lower temperature can be carried out, and hence a burden on glass manufacturing equipment such as a melting furnace is reduced more, and the bubble quality of glass is improved more easily. That is, as the temperature at 10^(2.5) dPa·s becomes lower, the manufacturing cost of the tempered glass is more likely to be reduced. Herein, the “temperature at 10^(2.5) dPa·s” can be measured by, for example, a platinum sphere pull up method. It should be noted that the temperature at 10^(2.5) dPa·s corresponds to a melting temperature. In addition, an increase in the content of an alkali metal oxide, alkaline earth metal oxide, B₂O₃, ZnO, or TiO₂ in the glass composition or a reduction in the content of SiO₂ or Al₂O₃ in the glass composition is likely to lower the temperature at 10^(2.5) dPa·s.

The tempered glass of the present invention has a liquidus temperature of preferably 1,200° C. or less, 1,150° C. or less, 1,100° C. or less, 1,080° C. or less, 1,050° C. or less, 1,020° C. or less, or 1,000° C. or less. It should be noted that as the liquidus temperature becomes lower, the devitrification resistance and formability are improved more. It should be noted that the liquidus temperature is easily decreased by increasing the content of Na₂O, K₂O, or B₂O₃ in the glass composition or by reducing the content of Al₂O₃, Li₂O, MgO, ZnO, TiO₂, or ZrO₂ in the glass composition.

The tempered glass of the present invention has a liquidus viscosity of preferably 10^(4.0) dPa·s or more, 10^(4.4) dPa·s or more, 10^(4.8) dPa·s or more, 10^(5.0) dPa·s or more, 10^(5.3) dPa·s or more, 10^(5.5) dPa·s or more, 10^(5.7) dPa·s or more, 10^(5.6) dPa·s or more, or 10^(6.0) dPa·s or more. It should be noted that as the liquidus viscosity becomes higher, the devitrification resistance and formability are improved more. Further, the liquidus viscosity is easily increased by increasing the content of Na₂O or K₂O in the glass composition or by reducing the content of Al₂O₃, Li₂O, MgO, ZnO, TiO₂, or ZrO₂ in the glass composition.

The tempered glass of the present invention has a crack resistance before tempering treatment of preferably 100 gf or more, 200 gf or more, 300 gf or more, 400 gf or more, 500 gf or more, 600 gf or more, 700 gf or more, 800 gf or more, 900 gf or more, or 1,000 gf or more. As the crack resistance increases, a surface flaw is less liable to be created on the tempered glass, and hence the mechanical strength of the tempered glass is less liable to lower. In addition, the mechanical strength is less liable to vary. In addition, when the crack resistance is high, a lateral crack is hardly generated at the time of post-tempering cutting such as scribe cutting, and hence the post-tempering scribe cutting can be easily performed appropriately. As a result, the manufacturing cost of a device can be easily reduced.

Herein, the “crack resistance” refers to a load at a crack generation rate of 50%. In addition, the “crack generation rate” refers to a value measured as described below. First, in a constant temperature and humidity chamber kept at a humidity of 30% and a temperature of 25° C., a Vickers indenter set to a predetermined load is driven into a glass surface (optically polished surface) for 1.5 seconds, and 15 seconds after that, the number of cracks generated from the four corners of the indentation is counted (4 per indentation at maximum). The indenter is driven in this manner 20 times, the total number of generated cracks is determined, and then the crack generation rate is determined by the following expression: total number of generated cracks/80×100.

When the tempered glass of the present invention is immersed in a 10 mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, its mass reduction is preferably 150 mg/cm² or less, 100 mg/cm² or less, 50 mg/cm² or less, 45 mg/cm² or less, 40 mg/cm² or less, 30 mg/cm² or less, 20 mg/cm² or less, 10 mg/cm² or less, 5 mg/cm² or less, 3 mg/cm² or less, 1 mg/cm² or less, 0.8 mg/cm² or less, 0.7 mg/cm² or less, 0.6 mg/cm² or less, 0.5 mg/cm² or less, 0.4 mg/cm² or less, 0.3 mg/cm² or less, 0.2 mg/cm² or less, or 0.1 mg/cm² or less. As the mass reduction reduces, the tempered glass becomes less liable to be corroded by a chemical. Thus, the tempered glass can be appropriately treated in a photoresist step or the like.

A tempered glass sheet of the present invention comprises the tempered glass described above. Thus, technical features (suitable characteristics, suitable component ranges, and the like) of the tempered glass sheet of the present invention are the same as the technical features of the tempered glass of the present invention in principle, and hence detailed descriptions of the technical features of the tempered glass sheet of the present invention are omitted here.

The surface of the tempered glass sheet of the present invention has an average surface roughness (Ra) of preferably 10 Å or less, 8 Å or less, 6 Å or less, 4 Å or less, 3 Å or less, particularly 2 Å or less. As the average surface roughness (Ra) increases, the mechanical strength of the tempered glass sheet tends to become lower. Herein, the average surface roughness (Ra) refers to a value measured by a method in conformity with SEMI D7-97 “FPD Glass Substrate Surface Roughness Measurement Method.”

The tempered glass sheet of the present invention has a length dimension of preferably 500 mm or more, 700 mm or more, or 1,000 mm or more and a width dimension of preferably 500 mm or more, 700 mm or more, or 1,000 mm or more. An increase in the size of the tempered glass sheet enables the tempered glass sheet to be suitably used as a cover glass for the display portion of the display of a large-size TV or the like.

The sheet thickness of the tempered glass sheet of the present invention is preferably 2.0 mm or less, 1.5 mm or less, 1.3 mm or less, 1.1 mm or less, 1.0 mm or less, 0.8 mm or less, or 0.7 mm or less. Meanwhile, when the sheet thickness is excessively small, desired mechanical strength is difficult to obtain. Thus, the sheet thickness is preferably 0.1 mm or more.

In the tempered glass sheet of the present invention, it is preferred to attach a protective resin film onto at least one surface of the tempered glass sheet, and it is more preferred to attach the protective resin film onto each of both surfaces of the tempered glass sheet. A material for the protective resin film is preferably capable of being detachably attached onto the surface of the tempered glass sheet. With this, a situation in which a flaw is created in the surface of the tempered glass sheet during the transportation or shipment of the tempered glass sheet to lower the mechanical strength of the tempered glass sheet can be easily prevented. Further, in the case of, for example, forming a functional film such as a transparent conductive film on the surface of the tempered glass sheet, the protective resin film can be easily peeled from the surface of the tempered glass sheet. From the viewpoint of attachment efficiency, the size (longitudinal dimension×lateral dimension) of the protective resin film is preferably smaller than the size of the tempered glass sheet. From the viewpoint of preventing the tempered glass sheet from having a surface flaw, at least one of the longitudinal dimension and lateral dimension of the protective resin film is preferably set equal to or larger than that of the tempered glass sheet, and the surface of the tempered glass sheet is more preferably covered completely with the protective resin film. It should be noted that the thickness of the protective resin film is preferably smaller than the sheet thickness of the tempered glass sheet from the viewpoint of a packaging ratio or the like.

A tempered glass container of the present invention comprises the tempered glass described above. Thus, technical features (suitable characteristics, suitable component ranges, and the like) of the tempered glass container of the present invention are the same as the technical features of the tempered glass of the present invention in principle. Detailed descriptions of the technical features of the tempered glass container of the present invention are omitted here.

The tempered glass container of the present invention is preferably obtained by processing a glass tube into a glass container and then subjecting the glass container to tempering treatment. The glass tube preferably has an outer diameter dimension of from 5 to 50 mm, from 5 to 40 mm, or from 5 to 30 mm, and preferably has a thickness dimension of from 0.3 to 2 mm, from 0.3 to 1.5 mm, or from 0.4 to 1.5 mm.

A glass to be tempered of the present invention is a glass to be subjected to tempering treatment, comprising as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F. Thus, technical features (suitable characteristics, suitable component ranges, and the like) of the glass to be tempered of the present invention are the same as the technical features of the tempered glass of the present invention and the tempered glass sheet of the present invention in principle, and hence detailed descriptions of the technical features of the glass to be tempered of the present invention are omitted here.

The glass to be tempered of the present invention has a crack resistance of preferably 100 gf or more, 200 gf or more, 300 gf or more, 400 gf or more, 500 gf or more, 600 gf or more, 700 gf or more, 800 gf or more, 900 gf or more, or 1,000 gf or more. As the crack resistance increases, a surface flaw is less liable to be created on a tempered glass to be obtained, and hence the mechanical strength of the tempered glass is less liable to lower. In addition, the mechanical strength is less liable to vary. In addition, when the crack resistance is high, a lateral crack is hardly generated at the time of post-tempering cutting such as scribe cutting, and hence the post-tempering scribe cutting can be easily performed appropriately. As a result, the manufacturing cost of a device can be easily reduced.

In a glass sheet to be tempered of the present invention, it is preferred to attach a protective resin film onto at least one surface of the glass sheet to be tempered, and it is more preferred to attach the protective resin film onto each of both surfaces of the glass sheet to be tempered. A material for the protective resin film is preferably capable of being detachably attached onto the surface of the glass sheet to be tempered. With this, a situation in which a flaw is created in the surface of the glass sheet to be tempered during the transportation or shipment of the glass sheet to be tempered to lower the mechanical strength of the tempered glass sheet can be easily prevented. Further, in the case of, for example, subjecting the glass sheet to be tempered to ion exchange treatment, the protective resin film can be easily peeled from the surface of the glass sheet to be tempered. From the viewpoint of attachment efficiency, the size (longitudinal dimension×lateral dimension) of the protective resin film is preferably smaller than the size of the glass sheet to be tempered. From the viewpoint of preventing the glass sheet to be tempered from having a surface flaw, at least one of the longitudinal dimension and lateral dimension of the protective resin film is preferably set equal to or larger than that of the glass sheet to be tempered, and the surface of the glass sheet to be tempered is more preferably covered completely with the protective resin film. It should be noted that the thickness of the protective resin film is preferably smaller than the sheet thickness of the glass sheet to be tempered from the viewpoint of a packaging ratio or the like.

Specific examples of the case where the protective resin film is attached onto the glass sheet to be tempered are described below. As illustrated in FIG. 1 a, in such a manner that a protective resin film 1 having a rectangular shape is protruded beyond two parallel sides of a glass sheet to be tempered 2 having a rectangular shape and a protruding dimension a beyond each of the two sides is set to about 10 nam, the protective resin film 1 may be attached onto one surface, or each of both surfaces, of the glass sheet to be tempered 2. In addition, as illustrated in FIG. 1 b, in such a manner that the protective resin film 1 having a rectangular shape is protruded beyond only one side of the glass sheet to be tempered 2 having a rectangular shape and a protruding dimension b beyond the side is set to about 10 mm, the protective resin film 1 may be attached onto one surface, or each of both surfaces, of the glass sheet to be tempered 2. Further, as illustrated in FIG. 1 c, in such a manner that the four sides of the glass sheet to be tempered 2 having a rectangular shape are protruded beyond the protective resin film 1 having a rectangular shape, the protective resin film 1 may be attached onto one surface, or each of both surfaces, of the glass sheet to be tempered 2. In addition, as illustrated in FIG. 1 d, in such a manner that the protective resin film 1 having a rectangular shape is protruded beyond the four sides of the glass sheet to be tempered 2 having a rectangular shape, the protective resin film 1 may be attached onto one surface, or each of both surfaces, of the glass sheet to be tempered 2. It should be noted that the attachment states of the protective resin film 1 with respect to the glass sheet to be tempered 2 as described above may be similarly applied to the attachment state of the protective resin film with respect to the above-mentioned tempered glass sheet.

When the glass to be tempered of the present invention is subjected to ion exchange treatment in a KNO₃ molten salt (having no history of being used) at 430° C., it is preferred that the compression stress value of a compression stress layer in a surface thereof be 300 MPa or more and the thickness of the compression stress layer be 10 μm or more, it is more preferred that the compression stress of the surface thereof be 400 MPa or more and the thickness of the compression stress layer be 15 μm or more, and it is particularly preferred that the compression stress of the surface thereof be 500 MPa or more and the thickness of the compression stress layer be 15 μm or more.

The glass to be tempered of the present invention preferably has a ratio CS₂/CS₁ of a compression stress value CS₂ to a compression stress value CS) of 0.7 or more, 0.71 or more, 0.72 or more, or 0.73 or more, the compression stress value CS₁ being determined for a compression stress layer that is obtained by subjecting the glass to be tempered to ion exchange treatment in a potassium nitrate molten salt free of a history of being used, the compression stress value CS₂ being determined for a compression stress layer that is obtained by subjecting the glass to be tempered to ion exchange treatment in a potassium nitrate molten salt comprising 20,000 ppm (by mass) of Na ions. With this, even when a deteriorated ion exchange solution is used, the ion exchange performance can be easily maintained. As a result, the replacement interval of the ion exchange solution can be lengthened.

When the ion exchange treatment is performed, the temperature of the KNO₃ molten salt is preferably from 400 to 550° C., and the ion exchange time is preferably from 0.5 to 10 hours, particularly preferably from 0.5 to 4 hours. Under the conditions, the compression stress layer can be properly formed easily. It should be noted that the glass to be tempered of the present invention has the above-mentioned glass composition, and hence the compression stress value and thickness of the compression stress layer can be increased without using a mixture of a KNO₃ molten salt and a NaNO₃ molten salt or the like.

The glass to be tempered, tempered glass, tempered glass container, and tempered glass sheet of the present invention can be produced as described below.

First, glass raw materials, which have been blended so as to have the above-mentioned glass composition, are loaded in a continuous melting furnace, are melted by heating at 1,500 to 1,650° C., and are fined. After that, the resultant is fed to a forming apparatus, is formed into, for example, a sheet shape or a tube shape, and is annealed. Thus, a glass sheet, a glass tube, or the like can be produced.

An overflow down-draw method is preferably adopted as a method of forming the glass sheet. The overflow down-draw method is a method by which a high-quality glass sheet can be produced in a large amount, and by which even a large-size glass sheet can be easily produced. In addition, the method allows flaws on the surface of the glass sheet to be reduced to the extent possible.

Various forming methods other than the overflow down-draw method may also be adopted. For example, forming methods such as a float method, a down draw method (such as a slot down method or a re-draw method), a roll out method, and a press method may be adopted.

In addition, as a method of forming a glass tube, it is preferred to adopt a down-draw method, an up-draw method, a Vello method, or a Danner method. Particularly from the viewpoint of production efficiency, the Danner method is preferably adopted. In this context, the Danner method is a method comprising winding molten glass on the surface of a rotating cylindrical refractory, allowing the glass to flow down to the end of the refractory, and drawing the glass out of the end of the refractory into a tube shape while blowing air into the glass. After that, the glass tube can be processed into the glass container through local heating with a gas burner. It should be noted that residual strain generated at the time of the processing can be removed by putting the glass tube into an annealing furnace.

Next, the resultant glass to be tempered is subjected to tempering treatment, thereby being able to produce a tempered glass. The resultant tempered glass may be cut into pieces having predetermined sizes before the tempering treatment, but the cutting is preferably performed after the tempering treatment from the viewpoint of the manufacturing efficiency of a device.

The tempering treatment is preferably ion exchange treatment. Conditions for the ion exchange treatment are not particularly limited, and optimum conditions may be selected in view of, for example, the viscosity properties, applications, thickness, inner tensile stress, and dimensional change of glass. The ion exchange treatment can be performed, for example, by immersing the glass to be tempered in a KNO₃ molten salt at 400 to 550° C. for 0.5 to 10 hours. Particularly when the ion exchange of K ions in the KNO₃ molten salt with Na components in the glass is performed, it is possible to form efficiently a compression stress layer in a surface of the glass.

It is preferred that an end surface of the glass sheet to be tempered be subjected to etching treatment and then the glass sheet to be tempered be subjected to ion exchange treatment to provide the tempered glass sheet. With this, the end surface is brought into a smooth state, and a compression stress layer is formed in such end surface. Accordingly, the mechanical strength, in particular, three-point bending strength, of the tempered glass sheet can be significantly enhanced. An etching liquid to be used in the etching treatment is preferably a solution comprising F, particularly preferably an aqueous solution comprising HF. With this, the end surface can be easily etched so as to be brought into a smooth state.

It is also preferred that an end surface of the glass sheet to be tempered be fire-polished and then the glass sheet to be tempered be subjected to ion exchange treatment to provide the tempered glass sheet. With this, the end surface is brought into a smooth state, and a compression stress layer is formed in such end surface. Accordingly, the mechanical strength, in particular, three-point bending strength, of the tempered glass sheet can be significantly enhanced.

It is also preferred that an end surface of the glass sheet to be tempered be subjected to polishing processing, in particular, chamfering processing and then the glass sheet to be tempered be subjected to ion exchange treatment to provide the tempered glass sheet. With this, the end surface is brought into a smooth state, and a compression stress layer is formed in such end surface. Accordingly, the mechanical, strength, in particular, three-point bending strength, of the tempered glass sheet can be significantly enhanced.

When the tempered glass sheet is cut, laser cutting or scribe cutting is preferably adopted. A CO₂ laser or a short-pulse laser is preferably used in the laser cutting. With this, an unintended crack is hardly developed at the time of the cutting.

When the tempered glass sheet is subjected to the scribe cutting, it is preferred that the depth of an initial cut (scribing cut) be larger than the thickness of the compression stress layer and the tempered glass sheet have an internal tensile stress of 100 MPa or less, 80 MPa or less, 70 MPa or less, 60 MPa or less, 40 MPa or less, 30 MPa or less, 25 MPa or less, 23 MPa or less, or 20 MPa or less. In addition, scribing is preferably started from one end of the tempered glass sheet or from a region at a distance of 5 mm or more therefrom, and the scribing is preferably stopped at a region at a distance of 5 mm or more from the other end of the tempered glass sheet. Further, a snapping step is preferably provided after the scribing. With this, an unintended crack is hardly generated at the time of the scribing, and hence the post-tempering scribe cutting can be easily performed appropriately. It should be noted that the internal tensile stress can be calculated by the following equation 1. For example, a wheel cutter having a protrusion on its outer circumference is preferably used for forming the scribing cut.

Internal tensile stress=(compression stress value of compression stress layer×thickness of compression stress layer)/{sheet thickness−2×(thickness of compression stress layer)}  <Equation 1>

It is preferred that after the glass sheet to be tempered has been subjected to ion exchange treatment to provide the tempered glass sheet, an end surface of the tempered glass sheet be subjected to etching treatment, and it is more preferred that after the glass sheet to be tempered has been subjected to ion exchange treatment to provide the tempered glass sheet, an end surface of the tempered glass sheet be subjected to polishing processing, in particular, chamfering process ing and then the end surface be subjected to etching treatment. With this, the end surface is brought into a smooth state, and hence even when the end surface has no compression stress layer formed therein, the mechanical strength, in particular, three-point bending strength, of the tempered glass sheet can be enhanced. An etching liquid to be used in the etching treatment is preferably a solution comprising F, particularly preferably an aqueous solution comprising HF. With this, the end surface can be easily etched so as to be brought into a smooth state.

EXAMPLES

The present invention is hereinafter described based on Examples. It should be noted that the following examples are merely illustrative. The present invention is by no means limited to these examples.

Tables 1 to 8 show examples of the present invention (sample Nos. 1 to 45).

TABLE 1 Example No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Glass SiO₂ 68.2 67.4 67.2 66.4 68.8 68.0 com- Al₂O₃ 11.6 12.2 11.6 12.3 11.6 12.3 position MgO 2.5 2.5 2.5 2.5 0.8 0.8 (mol %) B₂O₃ 4.9 5.1 6.0 6.0 5.2 5.2 Na₂O 11.3 11.4 11.3 11.4 12.4 12.5 K₂O 1.4 1.4 1.4 1.4 1.1 1.1 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 12.7 12.8 12.7 12.8 13.5 13.6 K₂O MgO + CaO + 2.48 2.47 2.48 2.50 0.78 0.81 SrO + BaO Li₂O + Na₂O + 15.20 15.24 15.19 15.26 14.29 14.39 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.16 0.16 0.16 0.16 0.05 0.06 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.24 0.26 0.26 0.28 0.24 0.26 SiO₂ Density (g/cm³) 2.39 2.39 2.38 2.38 2.39 2.39 α (×10⁻⁷/° C.) 74 75 75 75 77 78 Ps (° C.) 563 569 556 561 557 561 Ta (° C.) 615 624 607 614 607 614 Ts (° C.) 885 899 881 884 862 892 10⁴ dPa · s 1,323 1,330 1,305 1,322 1,323 1,343 (° C.) 10³ dPa · s 1,537 1,538 1,518 1,526 1,550 1,561 (° C.) 10^(2.5) dP · s 1,670 1,671 1,649 1,652 1,692 1,695 (° C.) TL (° C.) 1,139 >1,160 >1,160 >1,160 >1,160 1,160 LogηTL 5.1 <5.1 <4.9 <5.0 <4.9 5.1 (dPa · s) Chemical 0.3 0.7 0.7 1.4 0.3 0.5 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 838 867 826 845 871 906 DOL₁ (μm) 37 39 35 36 38 40 CS₂ (MPa) 598 624 610 620 647 670 DOL₂ (μm) 35 36 34 34 35 38 CS₂/CS₁ 0.71 0.72 0.74 0.73 0.74 0.74

TABLE 2 Example No. 7 No. 8 No. 9 No. 10 No. 11 No. 12 Glass SiO₂ 67.8 67.2 68.0 69.6 68.7 67.6 com- Al₂O₃ 11.6 12.3 11.5 10.8 10.8 10.8 position MgO 0.8 0.8 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 6.1 6.0 3.4 2.6 3.6 4.7 Na₂O 12.4 12.5 15.4 15.3 15.3 15.2 K₂O 1.1 1.1 0.0 0.0 0.0 0.0 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 13.5 13.6 15.4 15.3 15.3 15.2 K₂O MgO + CaO + 0.80 0.81 1.60 1.60 1.60 1.59 SrO + BaO Li₂O + Na₂O + 14.34 14.41 17.00 16.90 16.87 16.77 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.06 0.06 0.09 0.09 0.09 0.09 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.26 0.27 0.22 0.19 0.21 0.23 SiO₂ Density (g/cm³) 2.39 2.38 2.42 2.42 2.42 2.42 α (×10⁻⁷/° C.) 77 78 81 81 80 80 Ps (° C.) 551 556 560 562 557 553 Ta (° C.) 601 608 606 608 601 596 Ts (° C.) 856 873 835 840 824 810   10⁴ dPa · s 1,302 1,326 1,263 1,266 1,249 1,227 (° C.)   10³ dPa · s 1,529 1,545 1,487 1,499 1,478 1,454 (° C.) 10^(2.5) dPa · s 1,667 1,680 1,624 1,646 1,622 1,597 (° C.) TL (° C.) 1,032 1,141 981 979 963 940 LogηTL 5.8 5.1 5.9 6.0 6.0 6.0 (dPa · s) Chemical 0.5 0.9 0.3 0.1 0.1 0.2 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 855 887 909 821 846 853 DOL₁ (μm) 36 38 32 31 29 27 CS₂ (MPa) 639 661 695 652 645 664 DOL₂ (μm) 33 35 30 29 27 25 CS₂/CS₁ 0.75 0.74 0.76 0.79 0.76 0.78

TABLE 3 Example No. 13 No. 14 No. 15 No. 16 No. 17 No. 18 Glass SiO₂ 68.1 67.1 69.9 68.8 68.9 68.0 com- Al₂O₃ 11.5 11.6 10.9 10.8 11.5 11.5 position MgO 1.6 1.6 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 3.6 4.5 2.5 3.6 3.6 4.4 Na₂O 14.4 14.4 14.3 14.3 14.3 14.3 K₂O 0.7 0.7 0.7 0.7 0.0 0.0 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 15.1 15.1 15.0 15.0 14.3 14.4 K₂O MgO + CaO + 1.62 1.64 1.61 1.64 1.61 1.63 SrO + BaO Li₂O + Na₂O + 16.72 16.74 16.63 16.66 15.95 16.00 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.10 0.10 0.10 0.10 0.10 0.10 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.22 0.24 0.19 0.21 0.22 0.23 SiO₂ Density (g/cm³) 2.42 2.42 2.42 2.42 2.41 2.41 α (×10⁻⁷/° C.) 82 82 81 81 77 77 Ps (° C.) 558 554 561 556 568 561 Ta (° C.) 605 599 607 600 617 608 Ts (° C.) 840 826 843 827 864 846   10⁴ dPa · s 1,275 1,250 1,278 1,255 1,296 1,281 (° C.)   10³ dPa · s 1,503 1,474 1,506 1,486 1,519 1,504 (° C.) 10^(2.5) dPa · s 1,641 1,613 1,645 1,632 1,653 1,640 (° C.) TL (° C.) 940 953 1,001 1,006 960 973 LogηTL 6.4 6.1 5.9 5.6 6.5 6.2 (dPa · s) Chemical 0.3 0.6 0.1 0.5 0.1 0.3 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 860 863 816 828 860 831 DOL₁ (μm) 33 31 34 32 31 32 CS₂ (MPa) 651 655 623 624 673 662 DOL₂ (μm) 31 29 32 29 28 26 CS₂/CS₁ 0.76 0.76 0.76 0.75 0.78 0.80

TABLE 4 Example No. 19 No. 20 No. 21 No. 22 No. 23 No. 24 Glass SiO₂ 70.4 69.7 68.5 68.1 67.8 67.6 com- Al₂O₃ 10.7 10.8 11.4 11.4 11.5 11.4 position MgO 1.6 1.6 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 2.8 3.6 3.7 3.8 3.7 3.7 Na₂O 14.3 14.2 13.9 13.9 13.9 14.5 K₂O 0.0 0.0 0.7 1.0 1.4 1.0 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 14.3 14.3 14.6 15.0 15.3 15.5 K₂O MgO + CaO + 1.60 1.61 1.61 1.60 1.61 1.62 SrO + BaO Li₂O + Na₂O + 15.93 15.86 16.26 16.59 16.92 17.13 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.10 0.10 0.10 0.10 0.09 0.09 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.19 0.21 0.22 0.22 0.22 0.22 SiO₂ Density (g/cm³) 2.41 2.41 2.41 2.42 2.42 2.42 α (×10⁻⁷/° C.) 77 77 81 82 84 84 Ps (° C.) 570 564 564 560 554 556 Ta (° C.) 619 610 612 607 600 602 Ts (° C.) 865 847 856 846 836 830   10⁴ dPa · s 1,301 1,292 1,297 1,284 1,263 1,269 (° C.)   10³ dPa · s 1,530 1,520 1,522 1,511 1,491 1,495 (° C.) 10^(2.5) dPa · s 1,673 1,658 1,657 1,656 1,630 1,636 (° C.) TL (° C.) 1,021 1,034 974 964 957 967 LogηTL 5.9 5.6 6.3 6.2 6.2 6.1 (dPa · s) Chemical 0.3 0.1 0.2 0.2 0.3 0.4 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 830 845 903 893 873 882 DOL₁ (μm) 32 30 34 35 37 35 CS₂ (MPa) 645 649 674 656 639 651 DOL₂ (μm) 30 27 32 33 35 33 CS₂/CS₁ 0.78 0.77 0.75 0.75 0.73 0.74

TABLE 5 Example No. 25 No. 26 No. 27 No. 28 No. 29 No. 30 Glass SiO₂ 67.4 67.5 66.6 66.8 66.3 67.4 com- Al₂O₃ 11.7 11.7 11.6 11.8 11.6 10.9 position MgO 1.6 1.6 1.6 1.6 0.8 0.8 (mol %) B₂O₃ 3.5 3.2 3.5 3.1 6.3 6.3 Na₂O 14.4 15.2 15.4 15.2 13.8 13.4 K₂O 1.3 0.7 1.0 1.3 1.1 1.0 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 15.7 15.9 16.5 16.5 14.9 14.5 K₂O MgO + CaO + 1.64 1.64 1.64 1.66 0.82 0.81 SrO + BaO Li₂O + Na₂O + 17.35 17.59 18.11 18.19 15.73 15.28 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.09 0.09 0.09 0.09 0.05 0.05 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.23 0.22 0.23 0.22 0.27 0.25 SiO₂ Density (g/cm³) 2.43 2.43 2.44 2.44 2.40 2.41 α (×10⁻⁷/° C.) 85 85 86 88 82 79 Ps (° C.) 552 552 549 550 542 545 Ta (° C.) 597 596 592 593 586 588 Ts (° C.) 826 817 808 815 805 803   10⁴ dPa · s 1,282 1,273 1,233 1,257 1,223 1,229 (° C.)   10³ dPa · s 1,504 1,494 1,459 1,479 1,458 1,466 (° C.) 10^(2.5) dPa · s 1,645 1,633 1,599 1,616 1,607 1,622 (° C.) TL (° C.) 908 923 909 893 977 986 LogηTL 6.6 6.4 6.4 6.7 5.6 5.6 (dPa · s) Chemical 0.6 0.6 0.7 0.7 1.0 0.5 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 871 879 849 855 871 858 DOL₁ (μm) 36 33 35 36 32 31 CS₂ (MPa) 645 659 636 634 653 632 DOL₂ (μm) 35 32 32 35 30 30 CS₂/CS₁ 0.74 0.75 0.75 0.74 0.75 0.74

TABLE 6 Example No. 31 No. 32 No. 33 No. 34 No. 35 No. 36 Glass SiO₂ 68.3 65.9 66.7 67.3 64.8 65.6 com- Al₂O₃ 10.3 11.6 11.0 10.3 11.6 11.0 position MgO 0.8 0.8 0.8 0.8 0.8 0.8 (mol %) B₂O₃ 6.1 7.1 7.0 7.2 8.1 8.0 Na₂O 13.4 13.5 13.3 13.3 13.5 13.5 K₂O 1.0 1.0 1.0 1.0 1.0 1.0 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 14.4 14.5 14.4 14.3 14.5 14.5 K₂O MgO + CaO + 0.79 0.82 0.82 0.81 0.82 0.82 SrO + BaO Li₂O + Na₂O + 15.21 15.36 15.20 15.13 15.35 15.31 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.05 0.05 0.05 0.05 0.05 0.05 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.24 0.28 0.27 0.26 0.30 0.29 SiO₂ Density (g/cm³) 2.41 2.40 2.40 2.40 2.39 2.40 α (×10⁻⁷/° C.) 79 80 80 79 80 80 Ps (° C.) 546 541 540 540 535 535 Ta (° C.) 589 585 583 582 578 577 Ts (° C.) 799 804 793 786 793 783   10⁴ dPa · s 1,206 1,226 1,214 1,190 1,224 1,194 (° C.)   10³ dPa · s 1,446 1,457 1,453 1,427 1,450 1,430 (° C.) 10^(2.5) dPa · s 1,595 1,603 1,601 1,578 1,586 1,578 (° C.) TL (° C.) 967 985 984 942 992 943 LogηTL 5.6 5.6 5.5 5.7 5.5 5.7 (dPa · s) Chemical 0.2 1.3 0.8 0.4 15.3 1.2 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 830 870 843 823 850 824 DOL₁ (μm) 30 31 31 28 30 29 CS₂ (MPa) 615 651 637 619 642 631 DOL₂ (μm) 28 30 28 27 28 28 CS₂/CS₁ 0.74 0.75 0.75 0.75 0.75 0.77

TABLE 7 Example No. 37 No. 38 No. 39 No. 40 No. 41 No. 42 Glass SiO₂ 66.6 68.8 69.4 67.1 67.9 69.0 com- Al₂O₃ 10.3 10.8 10.2 11.5 10.9 10.2 position MgO 0.8 1.6 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 7.8 3.6 3.7 4.6 4.5 4.4 Na₂O 13.3 14.3 14.3 14.4 14.2 14.0 K₂O 1.0 0.7 0.7 0.7 0.7 0.6 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 14.3 15.0 15.0 15.1 14.9 14.7 K₂O MgO + CaO + 0.82 1.64 1.62 1.65 1.65 1.65 SrO + BaO Li₂O + Na₂O + 15.11 16.68 16.60 16.77 16.56 16.31 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.05 0.10 0.10 0.10 0.10 0.10 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/ 0.27 0.21 0.20 0.24 0.23 0.21 SiO₂ Density (g/cm³) 2.40 2.42 2.42 2.42 2.42 2.42 α (×10⁻⁷/° C.) 79 82 81 81 81 80 Ps (° C.) 536 557 556 552 553 533 Ta (° C.) 578 602 600 596 597 596 Ts (° C.) 779 830 825 822 818 812   10⁴ dPa · s 1,168 1,281 1,254 1,250 1,267 1,284 (° C.)   10³ dPa · s 1,402 1,511 1,485 1,475 1,494 1,515 (° C.) 10^(2.5) dPa · s 1,554 1,656 1,629 1,615 1,636 1,662 (° C.) TL (° C.) 930 928 947 956 930 949 LogηTL 5.7 6.5 6.2 6.0 6.3 6.1 (dPa · s) Chemical 0.9 0.1 0.1 0.5 0.2 0.1 resistance [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 812 876 850 909 886 856 DOL₁ (μm) 27 32 32 32 30 30 CS₂ (MPa) 616 652 622 672 652 642 DOL₂ (μm) 25 30 29 29 29 27 CS₂/CS₁ 0.76 0.74 0.73 0.74 0.74 0.75

TABLE 8 Example No. 43 No. 44 No. 45 Glass SiO₂ 66.0 66.9 67.7 composition Al₂O₃ 11.5 10.9 10.2 (mol %) MgO 1.6 1.6 1.6 B₂O₃ 5.7 5.6 5.5 Na₂O 14.4 14.2 14.1 K₂O 0.7 0.7 0.6 SnO₂ 0.1 0.1 0.1 Li₂O + Na₂O + K₂O 15.1 14.9 14.8 MgO + CaO + SrO + BaO 1.65 1.66 1.65 Li₂O + Na₂O + K₂O + MgO + 16.72 16.54 16.44 CaO + SrO + BaO MgO/(Li₂O + Na₂O + K₂O + 0.10 0.10 0.10 MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/SiO₂ 0.26 0.25 0.23 Density (g/cm³) 2.42 2.42 2.42 α (×10⁻⁷/° C.) 82 80 80 Ps (° C.) 549 547 54 6 Ta (° C.) 592 590 588 Ts (° C.) 811 809 796 10⁴ dPa · s (° C.) 1,239 1,239 1,250 10³ dPa · s (° C.) 1,464 1,467 1,478 10^(2.5) dPa · s (° C.) 1,600 1,608 1,624 TL (° C.) 944 959 966 logηTL (dPa · s) 6.0 5.9 5.8 Chemical resistance 0.8 0.5 0.2 [10 mass % hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 903 898 844 DOL₁ (μm) 30 30 28 CS₂ (MPa) 671 655 629 DOL₂ (μm) 27 27 26 CS₂/CS₁ 0.74 0.73 0.75

Each of the samples in the tables was produced as described below. First, glass raw materials were blended so as to have glass compositions shown in the tables, and melted at 1,600° C. using a platinum pot. The time period of the melting was set to 21 hours. Thereafter, the resultant molten glass was cast on a carbon plate and formed into a sheet shape. The resultant glass sheet was evaluated for its various properties.

The density is a value obtained through measurement by a known Archimedes method.

The thermal expansion coefficient α is a value obtained through measurement of an average thermal expansion coefficient in a temperature range of from 30 to 380° C. using a dilatometer.

The strain point Ps and the annealing point Ta are values obtained through measurement based on a method of ASTM C336.

The softening point Ts is a value obtained through measurement based on a method of ASTM C338.

The temperatures at the viscosities at high temperature of 10^(4.0) dPa·s, 10^(3.0) dPa·s, and 10^(2.5) dPa·s are values obtained through measurement by a platinum sphere pull up method.

The liquidus temperature TL is a value obtained through measurement of a temperature at which crystals of glass are deposited after glass powder that passes through a standard 30-mesh sieve (sieve opening: 500 μm) and remains on a 50-mesh sieve (sieve opening: 300 μm) is placed in a platinum boat and then kept for 24 hours in a gradient heating furnace.

The liquidus viscosity log η_(n), is a value obtained through measurement of a viscosity of glass at the liquidus temperature by a platinum sphere pull up method.

The chemical resistance is a mass reduction after immersion in a 10 mass % aqueous hydrochloric acid solution at 80° C. for 24 hours. The mass reduction of each sample was measured as described below. First, the mass and surface area of each sample before its immersion in the aqueous hydrochloric acid solution were measured. Next, each sample was immersed in the aqueous hydrochloric acid solution, and then the mass of each sample was measured. Finally, the mass reduction was calculated by the following expression: (mass before immersion-mass after immersion)/(surface area before immersion).

As evident from Tables 1 to 8, each of the samples had a density of 2.44 q/cm³ or less and a thermal expansion coefficient of 88×10⁻⁷/° C. or less. Further, each of the samples has a liquidus viscosity of 10^(4.0) dPa·s or more, thus being able to be formed into a sheet shape by the overflow down-draw method, and moreover, has a temperature at 10^(2.5) dPa·s of 1,695° C. or less. This is considered to allow a large number of glass sheets to be produced at low cost with high productivity.

Subsequently, ion exchange treatment was performed through immersion in a KNO₃ molten salt (having no history of being used) at 430° C. for 4 hours for each of the samples both surfaces of each of which had been subjected to optical polishing. After completion of the ion exchange treatment, the surface of each of the samples was washed. Then, the stress compression value (CS₁) and thickness (DOL₁) of a compression stress layer in the surface were calculated from the number of interference fringes and each interval between the interference fringes, the interference fringes being observed with a surface stress meter (FSM-6000 manufactured by Toshiba Corporation). In the calculation, the refractive index and optical elastic constant of each of the samples were set to 1.50 and 31 [(nm/cm)/MPa], respectively. It should be noted that the glass compositions of a surface layer of glass before and after tempering treatment are different from each other microscopically, but the glass composition of the glass as a whole is not substantially changed after the tempering treatment as compared to that before the tempering treatment.

In addition, ion exchange treatment was performed through immersion in a KNO₃ molten salt (containing 20,000 ppm (by mass) of Na ions) at 430° C. for 4 hours for each of the samples both surfaces of each of which had been subjected to optical polishing. After completion of the ion exchange treatment, the surface of each of the samples was washed. Then, the stress compression value (CS₂) and thickness (DOL₂) of a compression stress layer in the surface were calculated from the number of interference fringes and each interval between the interference fringes, the interference fringes being observed with a surface stress meter (FSM-6000 manufactured by Toshiba Corporation). In the calculation, the refractive index and optical elastic constant of each of the samples were set to 1.50 and 31 [(nm/cm)/MPa], respectively.

As evident from Tables 1 to 8, when each sample was subjected to ion exchange treatment in the KNO₃ molten salt free of a history of being used, its compression stress layer had a compression stress value of from 812 to 909 MPa and a thickness of from 27 to 40 μm. In addition, when each sample was subjected to ion exchange treatment in the KNO₃ molten salt comprising 20,000 ppm (by mass) of Na ions, its compression stress layer had a compression stress value of from 598 to 695 MPa and a thickness of from 25 to 38 μm. Further, the CS₂/CS₁ is from 0.71 to 0.80, indicating that the ion exchange performance does not significantly change even when a deteriorated KNO₃ molten salt is used.

INDUSTRIAL APPLICABILITY

The tempered glass and tempered glass sheet of the present invention are suitable for a cover glass for a cellular phone, a digital camera, a PDA, or the like, or a glass substrate for a touch panel display or the like. Further, the tempered glass container of the present invention is suitable for a container for pharmaceuticals. In addition, the tempered glass and tempered glass sheet of the present invention can be expected to find use in applications requiring high mechanical strength, for example, a window glass, a substrate for a magnetic disk, a substrate for a flat panel display, a cover glass for a solar battery, a cover glass for a solid image pick-up element, and tableware, in addition to the above-mentioned applications.

REFERENCE SIGNS LIST

-   -   1 protective resin film     -   2 glass sheet to be tempered 

1. A tempered glass having a compression stress layer in a surface thereof, comprising as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 2. The tempered glass according to claim 1, comprising as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 0.1 to 2.5% of MgO, and 0 to 2.5% of MgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 3. The tempered glass according to claim 1, comprising as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0.01 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, and 0.1 to 2.5% of MgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 4. The tempered glass according to claim 1, comprising as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 5. The tempered glass according to claim 1, comprising as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 6. The tempered glass according to claim 1, comprising as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 7. The tempered glass according to claim 1, wherein the tempered glass has a density of 2.45 g/cm³ or less.
 8. The tempered glass according to claim 1, wherein when the tempered glass is immersed in a 10 mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, a mass reduction, which is a value obtained by subtracting a mass of the tempered glass after the immersion from a mass of the tempered glass before the immersion and dividing a result of the subtraction by a surface area of the tempered glass before the immersion, is 40 mg/cm² or less.
 9. The tempered glass according to claim 1, wherein a compression stress value of the compression stress layer is 300 MPa or more, and a thickness of the compression stress layer is 10 μm or more.
 10. The tempered glass according to claim 1, wherein the tempered glass has a liquidus temperature of 1,200° C. or less.
 11. The tempered glass according to claim 1, wherein the tempered glass has a liquidus viscosity of 10^(4.0) dPa·s or more.
 12. The tempered glass according to claim 1, wherein the tempered glass has a temperature at 10^(4.0) dPa·s of 1,300° C. or less.
 13. The tempered glass according to claim 1, wherein the tempered glass has a thermal expansion coefficient in a temperature range of from 30 to 380° C. of 90×10⁻⁷/° C. or less.
 14. A tempered glass sheet, comprising the tempered glass according to claim
 1. 15. The tempered glass sheet according to claim 14, wherein the tempered glass sheet has a length dimension of 500 mm or more, a width dimension of 300 mm or more, and a thickness of from 0.1 to 2.0 mm.
 16. The tempered glass sheet according to claim 14, wherein the tempered glass sheet is formed by an overflow down-draw method.
 17. The tempered glass sheet according to claim 14, wherein the tempered glass sheet is used for a touch panel display.
 18. The tempered glass sheet according to claim 14, wherein the tempered glass sheet is used for a cover glass for a cellular phone.
 19. The tempered glass sheet according to claim 14, wherein the tempered glass sheet is used for a cover glass for a solar battery.
 20. A tempered glass sheet having a length dimension of 500 mm or more, a width dimension of 300 mm or more, and a thickness of from 0.1 to 2.0 mm, the tempered glass sheet comprising as a glass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F, the tempered glass sheet having a density of 2.45 g/cm³ or less, a compression stress value of a compression stress layer of 300 MPa or more, a thickness of the compression stress layer of 10 μm or more, a liquidus temperature of 1,200° C. or less, and a thermal expansion coefficient in a temperature range of from 30 to 380° C. of 90×10⁻⁷ or less.
 21. A tempered glass container, comprising the tempered glass according to claim
 1. 22. The tempered glass container according to claim 21, wherein the tempered glass container is used for a container for pharmaceuticals.
 23. A glass to be tempered, comprising as a glass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 24. The glass to be tempered according to claim 23, wherein when the glass to be tempered is immersed in a 10 mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, a mass reduction, which is a value obtained by subtracting a mass of the glass to be tempered after the immersion from a mass of the glass to be tempered before the immersion and dividing a result of the subtraction by a surface area of the glass to be tempered before the immersion, is 40 mg/cm² or less.
 25. The glass to be tempered according to claim 23, wherein the glass to be tempered has a ratio CS₂/CS₁ of a compression stress value CS₂ to a compression stress value CS₁ of 0.7 or more, the compression stress value CS₁ being determined for a compression stress layer that is obtained by subjecting the glass to be tempered to ion exchange treatment in a potassium nitrate molten salt free of a history of being used, the compression stress value CS₂ being determined for a compression stress layer that is obtained by subjecting the glass to be tempered to ion exchange treatment in a potassium nitrate molten salt comprising 20,000 ppm by mass of Na ions. 